The present application relates to a separator. In addition, the present application relates to a nonaqueous electrolyte battery having a separator between electrodes.
In recent years, attendant on the spreading of portable electronic information apparatuses such as cellphones, video cameras, notebook-sized personal computers, etc., it has been attempted to enhance the performance of these apparatuses and reduce them in size and weight. As power sources for these apparatuses, there have been used primary batteries which are disposable and secondary batteries which can be used repeatedly. From the viewpoint of good total balance of enhanced performance, reduced size, reduced weight, economy and the like, however, there has been an ever-increasing demand for nonaqueous electrolyte batteries, especially, lithium ion secondary batteries. In addition, further enhancement of performance and further reductions in size as to these apparatuses are being tried, and a further enhanced energy density is being demanded in regard of the nonaqueous electrolyte batteries such as lithium ion secondary batteries.
In order to achieve a drastic increase in the capacity of lithium ion secondary batteries, accordingly, an approach in which a metallic material or the like capable of being alloyed with lithium at the time of charging is used as a negative electrode active material in place of the carbonaceous negative electrode active materials used in the past has been proposed, as for example in Japanese Patent Laid-Open No. 2011-154901 and Japanese Patent Laid-Open No. 2011-023241 (hereinafter referred to as Patent Document 1 and Patent Document 2, respectively). Specifically, the use of silicon or tin or a compound thereof or the like as a metal-based negative electrode active material has been proposed. For instance, when used as a negative electrode active material in a lithium ion secondary battery, tin (Sn) is known to have a high theoretical capacity (about 994 mAh/g) which is much higher than the theoretical capacity of graphite (about 372 mAh/g). Furthermore, silicon (Si) has a much higher theoretical capacity (4199 mAh/g).